1. Field of the Invention
The present invention relates to the cleaning of objects, particularly substrates such as flat optic and flat panel display surfaces. More specifically, the present invention relates to methods and an apparatus for cleaning flat or curved planar surfaces by utilizing aqueous based cleaning solutions, deionized (D.I.) water rinsing and a drying process which take place sequentially as the surface to be cleaned is moved in a direction oppositely to the flowing fluid which performs these functions. Contaminant removal and rinsing are effected by flowing liquids, oppositely to the moving substrate, acoustical scrubbing and inducing surface tension film drainage forces oppositely to the moving flat or curved planar surfaces to be cleaned. The suggested modular in-line units performing these processes are of compact configuration and can be integrated, so as to enable cleaning to be adaptable to applications where continuous and in-line usage is desirable.
2. Description of the Prior Art
STELTER 4,004,045
BOK 4,370,356
VIJAN 4,696,885
BOK 5,270,079
LEENAARS et al. "MARANGONI DRYING: A NEW EXTREMELY CLEAN DRYING PROCESS"; Langmuir 1990, vol. 6, pp 1701-1703. "Method and Apparatus for Cleaning by Megasonics", EP Publication No. 0 603 008 A1, Jun. 22, 1994.
In the fabrication of flat display panels, continued miniaturization of pattern dimensions with the resultant increase in pattern densities, and the increase in panel sizes are occurring at a rapid pace and will continue, as quickly as improved technologies are developed. It is well documented that the trend to smaller feature sizes is significantly more sensitive to the population of submicron and micron-sized particulate materials and both organic and inorganic contaminant films. Unforturnately, these smaller particle sizes are extremely difficult to remove from surfaces due to the strong adhesive bonds, including van der Waals forces, that tenaciously hold these small particulate materials to the surface of the panel.
Almost all aspects of flat panel display processing steps which include handling, processing, diagnostic measuring and storage are potential sources of contamination. Such contamination may consist of particulate materials, organic materials, metallic impurities, inorganic salts and native oxides, as well as absorbed gaseous and liquid molecules. Aqueous based cleaning agents are necessary to remove several contaminant challenges and are desirable due to governmental regulatory concerns associated with organic based solvents. Cost effective and improved cleansing processing equipment capable of dislodging and removing these several categories of contaminants is desired in order to meet the higher performance standards for flat panel fabrication processes. The use of aqueous cleaning and dionized water rinsing liquids provide important advantages in reducing aqueous fluid consumption and waste water effluent quantities.
Present wet process cleaning methods are most often batch processes which involve the immersing of objects within a bath of cleaning fluid and exposing the object to ultrasonic and megasonic acoustical pressure waves in order to dislodge and remove particulate materials and, also, to accelerate the dissolution rate of organic and inorganic contaminant films. Ultrasonic transducers vibrating at frequencies between about 10 to 80 KHz are effective for particles larger than 1 micron. Megasonic transducers vibrate at higher frequencies ranging for 0.8 to 6 MHz and are useful in penetrating the surface/liquid interfacial boundary layers to dislodge particles smaller than 1 micron. The operation of ultrasonic and megasonic cleaning systems within a batch processor requires additional handling when integrated within an in-line continuous processing system. This additional handling increases the likelihood of contaminant reattachment to clean surfaces.
Aqueous cleaning and subsequent dionized rinsing of surfaces to be cleaned in a batch process mode entail a relatively high fluid usage and, as a consequence, proportionately high waste generation volumes. Accordingly, most batch cleaning systems stack the panel surfaces in a parallel arrangement. As a result, the removal of surface contaminants in the region between the passages of the closely stacked surfaces requires substantial fluid recirculation, in addition to considerable liquid makeup volumes to prevent the redepositing of dissolved and suspended impurities.
One particularly useful method for cleaning flat panels is described in EP 0 603 008 which addresses the removal of submicron-sized particulate materials and other soluble contaminants. Therein the utilization of megasonic pressure waves causes the upper surface of liquid to rise as a weir above the upper ends of a reservoir, while contacting the substrate surface to be cleaned from below. The cleaning liquid fluid then flows over a weir into a second reservoir. In EP 0 603 008, the megasonic pressure waves are directed perpendicularly. Consequently, both cleaning liquid flow and acoustical vibrations are directed nearly equally towards both the leading edge and trailing edge weirs. As a result, the contaminants removed from the surface to be cleaned and those present within the contacting flowing fluid are uniformly concentrated in effluent flows over the leading and trailing edge weir surfaces. The trailing edge effluent flow which moves in the same direction as the surface to be cleaned serves to inhibit adhering film drainage from hydrophobic surfaces. This relative movement of the surface to be cleaned and the flowing of cleaning liquid contributes to increased adhering film thicknesses with a consequent increase in residual film drying time, as well as an increase in contaminant residue levels which are deposited after the evaporation of the rinse aqueous film. Furthermore, the teachings of EP 0 603 008 do not address the removal of contaminants of greater size than 1 micron and do not suggest the concept of integrating fluid cleaning, dionized water rinsing and drying processes within a sequential and compact configuration suitable for in-line process adaptability.
Accordingly, methods and apparatus are desired for cleaning flat or curved planar surfaces to remove micron and submicron-sized particulate materials, while solubilizing inorganic and organic contaminants.
Methods and apparatus are desired that promote the nearly complete drainage of rinsing liquids from the surface to be cleaned, so as to accelerate drying rates and enhance cleanliness levels by minimizing the deposition of contaminant residues dissolved in rinse water films.
Methods and apparatus are desired for the integration of the cleaning, rinsing and drying operations within a sequential and compact configuration that can be readily adapted to in-line deployment in the several processing steps involved in the fabrication of flat optic and panel display surfaces.
In addition, methods and apparatus which provide high levels of surface cleanliness, while substantially diminishing the requirements for aqueous cleaning liquid and dionized water usage and, consequent, waste water effluent quantities are desired to reduce processing costs.